Thermal printer



Dec. 22, 1959 H. EPSTEIN El'AL THERMAL PRINTER 7 Sheets-Sheet 2 Filed April 25, 1955 INVENTORS. HERMAN EPSTEIN ROBERT R. TARBUCK ATTORNEY Dec. 22, 195 9 I H. EPSTEIN ETAL 2,917,996

THERMAL PRINTER 7 Sheets-Sheet 3 Filed April 25, 1955 INVENTORS.

HERMAN EPSTEIN ROBERT R. TARBUCK ATTORNEY Dec. 22, 1959 H. EPSTEIN ETAL THERMAL PRINTER '7 Sheets-Sheet 4 Filed April 25, 1955 TIMING DIAGRAM 'OF CAMSHAFT ROTATION DISENGAGED ADV. WHEEL INVENTORS H HERMAN EPSTEIN ROBERT R. TARBUCK PAPER ADVANCE PAWL INTERPOSER DETENT E R W G W T W R P ATTORNEY Dec. 22, 1959 H. EPSTEIN ETAL THERMAL PRINTER 7 Sheets-Sheet 5 Filed April 25, 1955 ATTORNEY INVENTORS. HERMAN EPSTEIN ROBERT R. TARBUCK Dec. 22, 1959 H. EPSTEIN ETAL 2,917,996

THERMAL PRINTER Filed April 25, 1955 '7 Sheets-Sheet 6 IIIO OOOI INVENTORS. HERMAN EPSTEIN ROBERT R. TAR K THERMAL PRINTER Herman Epstein and'Robert Ra' Tarbuck, WestChester, Paa, assignors .to BurroughsCorp pration, Detroit," Mich,

a corporation of. Michigan Application-April 25, 1955; S'ri al No. 503,668

5.Claims.i (Cl. 101-93) This invention relates to printing, and'more particularly to an improved apparatus forhigh' speed printing wherein heated styli are selectivelycontrolled for making discrete intelligible characters upon a'recordable surface.

Many high speed printers utilize the force generated by a'plurality of impact hammers to accomplishthe print ing. Such printers,requirerelatively large impact forces and. accordingly require'heavier driving apparatus and heavier andstrongeroperating parts; This not'only increases the: size: and'weight of such printers but their speed'is forthe'most 'partlimited by reason of the high inertia: of the heavy driving and printing members. Moreover, such high speed printers are not' generally adaptable for mobile usage. That is, these printers; because of :their weight 'andibulk, are not readily adaptable for use in small and confined quarters such as may be found'irr automobiles and'airplanes.

Inthose printers which depend for'theiroperationon type wheels or movable: printing matrices the problem of smudging or blurring'of theprinted'material is an ever present one.. Also, sincethetype'carryingbody or matrix moves withrespecttdsome-other member, such for example, as the printable material, ashortened parts life due to excessive wear=creates'a-considerable prob lem: The cost of replacing manyof the parts of commercially available high-speedprintersis relatively-high since the partsare usually speciali-zed onesandare'often intricately fabricatedfi Commercially available high speedprinting apparatus requires -ahigher voltage range than is' usually conveniently available which inturn necessitates the useof some sor-t'ofexternal power supply in order-to, boost the standard line voltageup to the operating level required by the printer.

High copy definition presents a considerable-problem when eithertheprintable material and/or'the'character bearing member are. moved at high speed. Further, if

both of the above mentioned members'must be moved with respect to each other, and indifferent directions, then,- any asynchronous movement of thesemembersis quite likely to cause blurring or smudging'.

Many of theavailable commercial printers are such highly specialized pieces "ofequipment that they do not lendthemselves well to other'uses than that for which they were originally developed; Conventional tape punching equipment is usually toolargeand too heavy for airborne operation and requires a large number of moving parts which are relatively expensive to'replace' and often difiicult'to maintain under'less than normal or ordinary operating circumstances;

An. important object, therefore, of the present invention is 7. to provide 4 anv improved: apparatus which overcomes the aforementioned problems; and at the same time accomplishesitheresult in a substantially simpler and more. economical manner. 5

Another important object ofthe; invention is to provide an improvedhigh speed'pn'nter capable of operating with low impact forces.and.requiringsubstantially. less power for operation.

* States Patent 0 till capable ofv high speed operation with low power and substantially reduced printing impact.

Another important object of the invention is to provide a high speed printer having an improved printingtechnique for transferring printing material from a carrier such as carbon paper, to the print receiving surface.

Another important object of the invention is to provide improved means of simple and eflicient design for adjusting the proximity of the printing styli or members to the print receiving surface.

Another important object of the invention is to provide a printing apparatus of the character aforesaid which provides a high degree of accessibility for inspection and replacement of parts and provides visible checking ofthe apparatus during its operation.

Another object of the invention is to provide an improved printing head wherein the elements are so designed and related that heat may be used for facilitatingthe transfer of the printing medium ontothe recordable surface, while the heat is prevented from smudging or otherwise impairing the recordable surface.

Still another important object of the'inventionisto,

provide a portable-mobile high-speed printer using. a direct rather than a linkage drive for actuating .the'printing plunger or styli.

Another object of the invention is toprovidedirect means for causing a pluralityof heated wire members toprint by transferring a transfer medium onto a printable medium through the application of moderate heat to the members and moderate striking force or impact by the members upon the two mediums.

Another important object of the invention is to provide a simple, reliable direct means for translating coded information, from a source external to the printer, into operating information for selectively actuating theprinten thereby.

Another important object of the invention is to providean improved high-speed direct wire drive printing apparatus wherein the printing is accomplished onlyrduring that portion of the operating cycle of the printer whenthe printable material is substantially at rest with respect 10- the printing elements or styli.

Another important. object of the invention is to provide: a direct wire drive printer utilizing a low level-non--- mechanical switching, thus resulting in a low overall power consumption.

A further important object of the invention is to provide a novel means in conjunction with the printing head for separating the carbon paper tape and the paper tape in the area of the printing head in order t0 producesmudge free printed copy.

In carrying out the objects hereinabove set forth, a

preferred embodiment of the present invention is provided with a printing-head comprising a plurality of sig nal responsive printing elements or styli. These elements are movably disposed in a compact assembly ormatrix and preferably heated in order to-function with the light striking force or impact previously mentioned. A print receiving medium and a transfer medium are superposed with respect to one another and are caused to be 'advanced over an exposed surface of the printing matrix.

Means is provided for adjusting the proximity of-these superposed mediums to the printing matrix. Each-one of the signal responsive elements isadapted to be actuated from an external source of signal information so that a preselected plurality of these members may-be instantaneously operated to form I discrete characters of intelligence.

The printing technique as set forth herein utilizes heat to reduce the force necessary to apply the transfer medium, such as carbon, upon a recording surface of paper to like material. To this end, each pin or stylus which provides the Contact for the printing operation is heated and maintained in such state during the operation of the printer. The heat thus generated makes the transfer medium more flowable and facilitates its transfer to the recording surface. As a result, only enough force is necessary for the contact of the styli as will bring the carbon paper and the print receiving surface into light momentary contact with one another. Thus, as it will become more apparent hereinafter, this slight contact enables the printing apparatus to be operated with lightweight parts and at relatively high speeds.

' In the practice of the invention, the duration of contact between the carbon paper and paper copy can be in the order of several milliseconds or less. The carbon paper backing is preferably of a light reflective material in order to reduce the effect of radiant heat and thus prevent an undue amount of the carbon coating from melting while the carbon paper is passing through the printing head. However, a relatively dense copy is obtainable. since virtually all of the carbon coating, i.e., the coating under the heated plunger area of contact, is transferred to the surface of the paper copy. In apparatus embodying this invention, a printing speed in the order of 70 characters per second has been obtained. A desirable temperature for the printing head is approximately 190. This particular temperature is variable depending upon the character of the carbon paper and other factors.

By the employment of improved means, the carbon paper and the print receiving paper copy are maintained in closely adjacent but spaced-apart relation to one another in and near the printing head and in such a manner that smudging of the paper copy is virtually eliminated.

These novel features of the invention, both as to its organization and method of operation, as well as additional objects and advantages thereof, will be understood more fully from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is a front elevational view of a plurality of racks of equipment illustrating one embodiment of the novel printing apparatus of the present invention;

Fig. 2 is an isometric view of the tape magazine and printer units of the apparatus of Fig. 1 showing the printing head drawer in withdrawn position and certain of the parts cut away in section in order to more clearly illustrate the construction and the relation of the parts to one another;

Fig. 3 is a top plan view, partly broken away in section, illustrating the printer unit of the invention and showing the printing head drawer in withdrawn position;

Fig. 4 is a view in side elevation, partly in section, the view being taken along the line 4--4 of Fig. 3,'showing the novel shim and clapper pivot for the wire actuating assembly of the invention and also showing the printing head drawer in its inserted, operating position;

Fig. 5 is an enlarged fragmentary view of the printing unit, partly in section, the view being taken along the line 55 of Fig. 3, illustrating the printer synchronizer and intermittent paper tape advance mechanism used with the present invention;

Fig. 6 is an enlarged view of a portion of the device shown in Fig. 4 showing the feed of the two tapes therethrough;

Fig. 7 is an enlarged view of the interposed rod construction of the invention;

Fig. 8 is a perspective view of a portion of the paper tape advance mechanism;

Fig. 8A is an enlarged isometric view of the interposer rod and actuating means;

Fig. 9 is an enlarged view of the interposed detent latch and actuating means of the invention;

Fig. 10 is a view in side elevation of the clapper pivot assembly for the wire plunger or pin actuating relays used with the present invention;

Fig. 11 is a timing diagram of the actuating cam shaft of the invention;

Fig. 12 is a side elevation, partially broken away, show ing the printing head with a portion of the carbon tape and the paper tape disposed thereacross;

Fig. 13 is an enlarged isometric view of the matrix arrangement of the printing wire guides;

Fig. 14 is an enlarged view of superimposed portions of the paper tape and carbon tape combination with the carbon tape partially turned back to illustrate the transfer of carbon upon the paper tape;

Fig. 15 is an end view of the matrix of printing wires and guides therefor shown in the same scale as the dotted character representation of Fig. 13;

Fig. 16 is a diagrammatic view of the printing head illustrating by numerals, the elements used therein; and

Fig. 17 is a schematic diagram illustrating the control circuits for the printing head by which selection of the printing elements thereof to form any particular character is accomplished in accordance with prearranged input information.

Fig. 17A is a schematic diagram illustrating one of the dual triodes which excite the wire actuating solenoids;

Fig. 18 is a schematic diagram illustrating the control circuits connecting the'pulse shaper units with the information feeding unit or computer by which synchronization of the printing unit with the computer is obtained.

The thermal printer of the present invention may be embodied in several small, light-weight, readily removable units. Fig. 1 shows a preferred embodiment of the invention mounted in a vertical rack with four such units in superimposed relation to one another. The four units of the illustrated embodiment of the invention comprise a tape magazine unit 10, a printer unit 12, a checking chassis unit 14 and a coding chassis unit 16. The supporting structure of each unit is generally alike. Referring to Fig. 2 and particularly to unit 10 shown therein, each unit has a front panel 18 and two parallel side members 2020. The four units are contained within a me tangular frame 22, Fig. 1, and are releasably secured thereto for removal from the front side thereof. For this purpose, the front panel of each unit projects beyond the side members as shown in Fig. 2 and are provided with holes or notches 24 through which bolts 26 extend for securing the unit to the main frame. Each one of the units is thus adapted to be easily replaced by like units or interchanged, insofar as its physical position or location is concerned, with any other one of the units, easily and quickly.

As viewed in Fig. 1 of the drawing, the first or top unit 10 contains the tape magazine and includes a removable section or drawer 28 having a plying unit, guide rollers, tension shock compensating leaf springs, and roll support reels for a printing medium and a transfer medium which, for the sake of illustration, may take the form of a pair of ribbons or tapes. The transfer medium tape 30 is preferably a substantially opaque ribbon having removable meltable deposit of carbon or like material 32 on one side thereof. In the practice of this invention it has been found highly desirable to substantially reduce, if not wholly prevent, radiant heat absorption by the carbon tape 30 by providing the opposite non-carbon side thereof with a light reflective or white surface. In the illustrated embodiment of the invention, the print receiving medium is a paper tape 34. The paper tape together with the carbon tape 30 are conducted from separate rolls in the tape magazine unit 10 through the medium of a plying unit generally indicated at 36 to the next lower printer unit 12 of the frame. A more specific description of the various elements of the tape magazine unit lo'jandttheirioperatingarelation tooneanother. follows hereinafter..-

Thor-secondiunitill-containszaprinter head having a plurality ofzsignal' responsive-means for imprinting intelligence characters serially onthe paper tape 34. The printerh'ead as hereinafter described, is constituted by narrow' reciprocable heatediwiresarranged in rows and columns ,to*form a=rnatrix. In the illustrated embodiment of the' invention-thirty-five-such printing wires are employedandtheyare' arranged in a x 7 matrix. Also contained-in the unit-12 is novel means for providing rapid interrnittent movement of the two tapes simultaneously; such as; at therate of thirty cycles per second, for example Thisis determinedby the speed of the printer driving mechanism and novel means for testing the operationof the tape advancing mechanism before supplying information to the' printer from the information sourcw The unit 121 also houses a suitable driving motor, synchronizingpulse generator; the tape advance mechanism; theheatediwireactuating plate assembly, and a retractibl'e printing section or drawer 38, all of which are described in more detail hereinafter.

The twotap es'30'and 34 are fed from the unit out through spaced apertures-40 and 42 respectively in the front'plate-of-the-tape carrying drawer 28 and conducted through the plying'device 36- for superposition on one another; The superposedtapes are thence conducted downwardly"and"-enter' the printer unit 12 through an aperture 44 in the-upper portion of the front plate of the printing; drawer 38. A' latch 46 is provided to releasablyqsecure' the drawer 38 to the printing unit 12 irr-flu'sh operating position in-the frame 22. An exposed knob 48'on thefrontface of the drawer 28 facilitates withdrawal of *the' drawer when the catch is released. The-two tapes; after the print-ing operation is finished, are discharged from an outletaperture 50 in the lower portionofthefrontplate' Of the'printing drawer. Means (not shown)"-maybe-provided for automatically causing tlie tapes to-be-separated from one another as they are discharged.

The checking chassis -unit 14, to be described more f1'1lly-late1"=on, comprises-a compact grouping of electrically interconnected circuitv components arranged to provide immcdiate and'continuous checks on the thermal printer'as well as to provide a means for locating faulty crystals'imthestwomatrices of the coding chassis unit. Meanssuch' as the-lamps 52' and 54 provide a visual indication of the on and off condition of the driving mechanism and the'printingwire heater element respectively.-'-

The" checking chassis unit 14'also includes a conventionalpower supply, such" as+250 volts, 6 volts AC. and 17'volts.' A 6.3 volt AtC. supply is used for the heaters of th'e various vacuum tubes used in the coding chassis unit-"16'." Acontrolled-"source-of alternating current is suppliedto the wire printing heating element. A thermistor (not shown) in thermal contact with the wire printing 'head providesa means for maintaining the temperatureof the printing--wires constant. Atoggle switch 55 at the lower-left of the'front panel of the unit 14 controls the-wireprinter driving motor. A standby switch 57 also on this front panel controls the bias voltages, as described more fully hereinafter. An initial starting switch is identified'on the unit 14 at 58. An indicator panel 56 contains thirty-five neon lamps arranged in a 5*x-7 "matrix; with eachlamp representing a different printing stylusof-jlthe printing head. Characters corresponding to the particularcode group chosen by means of- "the'-coded input may be exhibited on the lamp panel 56.

The lowermost orbottom unit 16 of the apparatus contains a decoding crystal matrix which, in the illustrative embodiment setforth in: Fig. 1, comprises 170 rectifieri crystals =:and l8 double triode vacuum tubes. This unitis adaptedtot-"utilize a; four-bit excess-three binary code and to print a choiceofsixteenicharacters serially in the aforementioned 5 x7 matrix form. Extensionofg,

the unit to accept a six-bitcodeand to otfera. choice-of; sixty-four characters involves theadditional interconnec tion of twenty more crystals in the encoding unit and. a. somewhat greater number ofcrystals in the decodingunit, depending upon design choice.

Mechanical switching of large currentsor voltagesv is. avoided by accomplishing the switching operation entirely through electronic means and at relatively low power. levels. Thus, none of the circuit elements are required.v to be large current handling devices. This factorproves. advantageous from the standpoint of component size, cost, and weight.

Referring more particularly to the isometric view of; Fig. 2, the printing unit drawer 38 is shownpartially, slidably withdrawn from the unit 12 by meansof guides: 60. A pair of tape reels 62 and 64- serving as the source; of supply for the two tapes30 and 34 are in side by side; relation for rotation about a common vertical shaft-662 in the unit 10. A pair of adjustable tape depletion sensing, arms 68 and 70 are movably mounted adjacent the tape; reels and secured to the shaft 72. One end of each one of the arms 68 and 70 makes a light but positive peeripheral contact with the exposed surfaces of the tapes. The opposite ends 74 and 76 of the sensing armsare: adapted to provide signal indications of the. depletion of. the tape supplies by means of a suitable alarm circuit interconnected therewith (not shown). The alarm cir-' cuit also includes a switch (not shown) which may be utilized to stop the information flow to the printer.

In order to conserve space and to simplify; the tape: feeding operation the paper tape 34 is superposed upon, the carbon tape 30 and jointly moved therewith. The plying unit 36, Figs. 1 and 2, includes a stationary pair; of smooth dowels or rods 78 and 80. The two rods are. disposed at approximately to one another and a slight distance in front of the front plate of the removable'tape magazine drawer 28. Idler pulleys 82 and 84 are secured to the face plate of the drawer 28 adjacent to the openings: 40 and 42 and disposed to guide the tapes to the dowel: pins in the manner shown in Figs. 1 and 2. 1

Drive means for the printing apparatus may be a suitably energized motor 90 provided with a drive shaft92. The motor drive shaft 92 is connected through a coupling, 94 to a cam shaft 96. The opposite end of the cam shaft 96 may be journaled in a bearing disposed in av wall member or otherwise supported for rotation.

Synchronization of the printing apparatus with the output from a source of signal information or intelligence is obtained by generating a pulse from the printer at a precise moment in its cycle of operation. This is accomplished by means of a rotary pulser, comprising a permanent magnet 1% (Figs. 2,3, and 4), in combination with a pair of stationary solenoids 102 and 104. The magnet 180 is secured to the drive shaft 92 by means of tie support 1% formed of two similar cross arms carrying a counterbalance weight 168 on the other end thereof. Rotation of the permanent magnet past the two solenoids generates an electromotive force (E.M.F.) in the form of pulses in the windings of the solenoids. These pulses are utilized to trigger suitable electrical circuits in the signal source which are interconnected with the printing apparatus. The windings of the two solenoids are electrically connected to the signal source (Figure 18). The solenoids are supported adjacent to the path of movement of the pulser magnet 100 at specific angular. positions in order to generatethe pulses at the desired time during each cycle as shown in Fig. 5. One of the two solenoids generates a Start pulse. The other solenoid generates a Stop pulse. The pulses start and stop the printing operation which will be described in detail later on. The angular position of the magnet 100 with respect to the camshaft 96 is adjustable so that theoptimum operatingposition can thus be obtained.

In carrying out the fundamental principle of the direct wire drive thermal printer, the invention comprises a printing matrix or head indicated generally at 110 (Figs. 2, 4, 6, and 12). The printing head 110 is a highly heatconductive aluminum block. The aluminum block acts as a support for the earlier mentioned heating element to be described in detail later. The head 110 is secured to a heat insulating retaining block 112.

The printing head 110 is provided with a small central aperture 114 preferably of rectangular configuration as shown. The block 110 supports a group of thirty-five guide tubes 116 which are compactly grouped together and enter the aperture 114. Before assembly as a matrix or head, each one of the guide tubes, fabricated from normally cylindrical stainless steel stock, is shaped along approximately the last inch of its length into a square shaped cross section as shown in Figs. 13 and 15. The thirty-five tubes 116 are then assembled into a x 7 matrix and projected through the opening 114 and clamped inposition. The tubes are lightly tinned with solder and when suitable heat is applied the tube assembly is soldered into a rigid 5 x 7 rectangular matrix.

An electrical heating element 118 (Figs. 6 and 12), such as a short length of resistance wire enclosed within a tubular ceramic insulator, is embedded in the printing head 110 so as to be in heat transfer relation with the extremities of the printing wires to be disposed therein. The retaining block 112 is also provided with an aperture 120 similar to the aperture 114 and registering therewith. The squared ends of the guide tubes 116 are thus extended through the two apertures which the cylindrical balance thereof extend rearwardly for connection to certain actuating devices presently to be described in detail.

The wire guide tubes 116 are ground off fiat and, as an assembly, may project slightly from the front side of the printing head block 110 as shown in Fig. 12. The tubes are fanned out in back across the top of a supporting shelf or plate 122 and its rearward extension 123 as shown in Figs. 3 and 4 and are secured thereto so that they lead into the retaining block 112 in positions relative to their printing positions in the printing head 110. Thirty-four wire actuating assemblies, each including a solenoid 124, are mounted on the underside of the plate 123. One solenoid (to be discussed later on) is omitted since it is not required in the printing of the 16 characters.

For the sake of convenience the solenoids 124 may be disposed in substantially parallel, arcuate, rows on the underneath surface of the shelf 123 (Figs. 4 and 5).

A printing element or stylus in the form of a wire 126 of very small circular cross sectional area extends through each one of the guide tubes 116 and projects from the opposite ends thereof. Each printing wire 126 is slidably disposed in its respective guide tube 116 so that it is reciprocable therein. The operating or printing end of each wire 126 normally terminates substantially flush with the squared end 117 of the guide sleeve in which it is enclosed. As shown in Fig. 4, the end of each guide tube remote from the retaining block 112 is fastened to the plate 123 by means of a screw 13% The wire in the tube, however, projects beyond this end of the tube and is connected to a movable part of one of the solenoids 124 previously mentioned.

As best shown in Figs. 4 and 10, each solenoid 124 of the illustrated embodiment of the invention comprises a coil 132 having a stationary core 134 and mounted on an L-shaped bracket 136, and the movable portion of the assembly including a clapper type armature 133 pivoted by pin 140 to the bracket and carrying a stainless steel arm 142 (Fig. extending alongside of the coil and terminating in a hollow extension or post 144. Each solenoid 124 is associated with the terminating end of a different one of the guide tubes 116 and mounted so that the extension or post 144 rises above the surface of the plate 123. For this purpose the plate is provided with an aperture 146 (Fig. 2) through which the post projects. The wire stylus associated with each solenoid isconnected to its post 144. As a result of the pivotal mounting of the arm 142 and the clapper armature 138, each post is capable of traversing a small arc toward and away from the front of the machine. The wire styli are so dimensioned lengthwise that when the post assumes a position away from the front of the machine the printing end of each wire is inoperatively enclosed within the heating block 116 and when the post is moved forward the printing end of each wire will project from the squared end of its guiding tube to perform its printing operation. Spring means is provided for resistingly yieldingly holding each post in its inoperative position. This may be accomplished, as shown, by connecting a coiled spring 148 to each movable post 144 and to a fixed post 149 secured in the plate 123 nearby. The spring is tensioned to pull the movable post rearwardly to its inoperative position. It is evident, however, that upon energization of each solenoid 124, its respective clapper 138 will be attracted and rocked about its pivot to cause the associated post and printing wire to move in the print operating direction against the tension of the spring.

A striking surface for the heated wires 126 is provided by means of a printing anvil which comprises a cylindrical member 150 having a slightly widened end portion 152 providing a flat surface disposed closely adjacent to the squared ends of'the guide tubes 116 mounted within the drawer 38, as best shown in Fig. 12. The anvil member 152 is adjustably mounted within the drawer 38. The flat end portion or surface of the anvil is adapted to be adjusted into close but spaced proximity to the printing head 110 and to provide the backup means for the heated wires 126 during the printing operation. The anvil member is provided with a reduced threaded shank extension 154 which projects through the front wall 156 of the drawer 38 and to which the knob 48 (Fig. 2) is attached. The shank is threadedly engaged with internal threads formed in an exteriorly squared block 158 which abuts the rear side of the front wall 156 of the drawer and is held from rotation by a side abutting element 160. The block 158 overlaps the anvil member to guide and steady the same. It is evident upon rotation of the threaded shank that the anvil surface may be advanced toward or away from the heating block 110. Suitable retaining nuts 162 and 164 may be provided respectively for the block 158 and the anvil member 150.

A spacer element 166, as shown in Figs. 4, 6 and 12, is secured to the cylindrical portion of the anvil 150. In the illustrated embodiment of the invention the spacer element functions as an interposing shim between the two tapes as they traverse the anvils flat surface and is preferably formed of flexible material such as a thin strip of phosphor bronze. For securement to the anvil member the shim or spacer element is provided with a U-shaped configuration. One of the parallel portions 168 of the shim is cut out or otherwise bifurcated and received within notch 169 cut in the cylindrical neck of the anvil member 150. The remaining parallel portion 170 of the shim overlies the flat surface of the anvil and between the same and the heating block 110. It is provided with an aperture 172 (Figs. 6 and 12) which is aligned with the aperture or slot 114 in the heating head 110. The paper tape 34 is fed between the flat surface of the anvil and the shim portion 170. The carbon tape 34 with the carbonized surface 32 facing the paper tape 34 and the white backing of the carbon tape facing toward the heating block 110 is fed between the portion 170 of the shim and the heating block 110. The carbon tape is thus disposed immediately in front of the heated ends of the printing wires or styli 116 but with carbon transfer side away from the wires.

Referring to Fig. 6 the two tapes 30 and 34 are shown passing over two sets of guide rollers. A first or front set of rollers 174 and 176 permits the tapes to follow a- -path-at-a 90 angle from the plying unit 36 into the printingunit drawer 38. T he'se'cond or rear set of rollers 178-and180isdisposed immediately above the heating block 110 and in line with the shim 166 so that the two tapesmay be fed along slightly separated paths verticallydownwardly to the shim. The shim maintains this spaced-apart relation of the tapes in the printing area. his now evident that when the apparatus is operated and the heated wires 116 are projected to form the intel-ligible characters, the heated wire ends will strike the carbontape30 and force tape through the aperture 172 in @the shim and cause the carbonized surface 32 of the tapeinto light contact with the paper tape 34 which is backed-up, at this point in its travel, by the fiat end portion of the anvil 158. Since the shim 166 permits printing-contactto be made only in the small area immediately adjacent .the heating member 110, the problem of smudging andablurring is completely avoided in this novel manner.

The elapsed time between the: contact of the heated wires,- with the carbon tape 30, and the carbon surface 32";withrthe paper tape 34, is dependent upon the thicknessrof. theshim. portion 170 and its proximity to the heating block 110. Enough contact time is provided between the-ends of the heated wires 126 and the carbon tape 30-for. suflicient heat to be transferred through the carbomtape-to melt a dot of carbon on its carbonized surfaceandwause transfer of the dot onto the paper tape 34. Only slight contact force of each heated wire 126 with;the tapes is necessary to cause substantially all of ;the carbonized area circumscribed by the end of each wireto. be melted and substantially completely transfcrljed to the paper tape 34.

During operation of the printer each one of the wires 11 6,isadapted to be projected from its normal non-print position at the surface of the printing head 110, to form by, -su ch projection a portion of a character such as a letter ofthe alphabet, a numeral, or other configuration. By proper selection of a plurality of printing wires and simultaneous operation thereof in a manner to be described presently, they may be combined when projected to form a discrete or recognizable character.

One side of each one of the windings (Fig. of the solenoids 124 is connected to a common point 13-]- by rneans of suitable leads. The other side of each one of. the solenoid windings is electrically connected into the plate circuit of a separate vacuum tube, the operation..,of which will also presently be described.

Figs. 5, 7, 8 and 9, together with Figs. 2 and 3, illustrate a novel paper tape advance mechanism used with the printing apparatus described herein. A rotary cam 182 is .secured to-the drive shaft 96, which in the present embodiment of the invention rotates at 1800 rpm. (30 cyclesper second). A spring loaded cam follower arm 184 ';lS pivotally mounted on stud 186 for oscillatable movement and carries a freely rotatable cam follower roller 188 which bears against the periphery of the cam 182 and is held thereagainst by the constraining action of. aspring 190. Continuous rotation of the shaft 96 causes the cam follower arm 184 to oscillate about its pivotal mounting due to the contact of the roller 188 with thecam 182 and the tension of the spring 190.

In the same unit of the machine as the drive shaft 96 and positioned parallel thereto is a tape advance shaft 192. One end of the shaft 192 is provided with a retractable spring clutch member 194 having a projecting coupling. pin 196. A coiled spring 198 encircles the tape advance shaft and yieldingly urges the clutch member from one end of the shaft. A tape advance sprocket wheel;,200 is normally rotatably coupled to the clutch 1 94 The sprocket wheel 200 is intermittently driven in one direction by the clutch 194 which in turn is similarly driven by the oscillating action of the cam follower arm 184.

T0 provide the intermittent movement of the clutch toothed wheel 204 fixed to'the shaft 192 and jointly rotatable-therewith. With each oscillation of the arm 184,

the pawl 202 comes back,- drops behind thenext tooth ofthe wheel 204, andthen pushes it to the next advanced position. In order to prevent areversal of direction ofmovement of the tape advance shaft 192, an anti-backupmember, for example, a leaf spring 206, is provided. The free end of the leaf spring 206 is adapted to drop behind" the teeth of the wheel 204-to prevent backward rotationof the wheel.

A detent actuating wheel 208, Figs. 3, 5,- 8, and9, is fixed to the driven shaft 192 intermediate the clutch 194 and the tape advance wheel 204. One arm 210 of an interposer detent latch 212, which is rockable about a' pin 213, is operatively disposed to engage the teeth of the wheel 20-8. The latch 212 is urged by a spring 214 to cause the arm 210 to engage the wheel 208. The opposite arm 216 of the detent latch engagesan interpos ing rod or pawl 218. An interposer actuating member- 220, Figs. 8 and 8A, having abifurcated end portion or yoke 222, is mounted for bodily movementparallel with the shaft 192 for the purpose described hereinafter. The interposer rod 218, as shown in Fig. 8A, is provided with two diametrically opposed grooves 224224 at one end thereof for receiving the yoked end of the interposer actuating member 220, as shown in Fig. 8. A notch 226: is also provided in the interposer rod 218 for receiving the arm 216 of the detent 212, as shown in Fig. 8. The

opposite end of the interposer rod 218 is shaped to ex-.

hibit a truncated formation 228, as shown in Fig. 7, so as to be received between two adjacent teeth of the wheel 204 and between the same and the pawl 202.

The opposite end of the pawl interposer actuating member 220 is operatively connected to the clapper type armature 230 of a paper tape advance actuating solenoidf 232 which is the extra solenoid before mentioned. The clapper 230 is held under tension by means of the spring 234 so as to urge the interposer rod in the direction to insert its truncated end between the pawl 202 and the wheel 204. Energization of the armature coil 232 will attract the clapper 230 and cause the interposer rod 218 to be moved in a plane parallel with the shaft 192 and out from between the pawl 202and two of the teeth of the paper tape advance wheel 204 thereby allowing the pawl 202 to fall into the vacated space and to advance the wheel 204 and its associated shaft when the cam follower arm is oscillated in one direction.

The tape advance wheel 200 is provided with a series of peripheral tape puncturing driving pins 236 which encircle the wheel. The tape drive wheel 200 is rotatably mounted on a shaft 238-in the printing unit drawer 38. The clutch 194 is constantly urged by its spring 198 into coupling engagement with the tape drive sprocket wheel 200. The torque transmitting pin 196 is adapted to be received within a recess (not shown) in the sprocket wheel 200.

Disengagement of the tape drive sprocket wheel from the clutch 194 is effected by a provision extending to theoutside of the unit including a laterally movable arm 240 forming part of the latch 46 previously described. The arm 240 is pivotally mounted intermediate its ends inside the unit on a stud 242. Spring means may be provided for constraining the arm into latched position. The inner end of the latch arm is pivotally connected to a link 244 which extends toward the clutch 194 and is provided with a yoke 246 which interengages the rear side of the clutch. Pivotal movement of the arm 240 will reciprocate the link and engage or disengage the clutch at will.

The printing unit drawer 38 is adapted to be withdrawn by means of a plurality of guide rods 60 slidably disposed in the unit 12. drawer to be pulled out after disengaging the clutch 194 The guide rods enable the 11 for tape threading and cleaning of the printing mechanisms. Insertion of the drawer in the unit 20 enables the clutch 194 to be engaged with the sprocket wheel 200 and permits the wheel to advance the two tapes when the tape advance shaft 192 rotates.

The tapes 30 and 34 may be imperforate when installed on their supply reels. In this event the projecting pins on the sprocket wheel 200 will puncture the tapes as the wheel is rotated and draw the tapes through the printing area. If desired, the tapes may be pre-punched with sprocket holes with which the pins 236 are engageable. The tWo tapes may be discharged from the drawer 38 through the opening 50 therein and kept from following the sprocket wheel therearound by a stripper plate 248 positioned adjacent to the tape discharge aperture 50, as shown in Fig. 6.

The timing of the mechanical and electrical compo nents of the novel printer may be explained by reference to the timing diagram set forth in Fig. 11. As before mentioned, the paper advance mechanism starts and stops the paper-carbon paper combination for each printing cycle; and the actual printing takes place while the tapes are at rest.

The printing cycle is started at the instant the start or on timing pulse is generated by the printer synchronizing rotary pulser, magnet 100 and the coil 102. This timing pulse is the signal to the input device, for example, an electronic computer, to feed a code group into the coding chassis unit 16, which in turn causes the specific set of vacuum tube grids to be placed at ground potential with respect to their cathodes, as will be hereinafter explained. These particular vacuum tubes excite the selected actuating solenoids 124 which push their respective heated wires 116 toward the anvil and cause the carbon tape to contact the paper tape and form a character corresponding to the particular code group input. A timing pulse is shown at reference in Fig. 11. Each of the excited solenoids requires approximately 6 milliseconds, or approximately the corresponding 60 of rotation of the drive shaft 96, to drive the wires out to the printing position in this embodiment. After 120 of camshaft rotation, the stop or off timing pulse generated by the rotary pulser magnet 100 and the second coil 104, is the signal to disable the input to the coding chassis unit 16 and return the vacuum tube inputs to 35 volts. This signal then allows the spring return of the particular wires which were chosen to print the characters. In other words, the printing wires are in the printing position from 60 to 120 of camshaft rotation. A full printing cycle in which a character is printed and the paper advances and stops comprises 360 of rotation.

The paper is advanced immediately after the actual printing and is at rest during the printing interval. This is indicated in the paper advance timing, Fig. 11, which shows that the paper starts moving at 310 and comes to rest at 60 just as the printing wires are driven to the paper surface in the succeeding cycle. The paper advance is controlled by the cam follower pawl 202 which begins to move at 240 in each cycle in which the paper is advanced. It should be noted that the paper actually starts moving after the pawls initial movement allowing for 70 of free pawl motion. After the pawl 202 posi tions the tapes for the next character, the pawl is reset by the spring 190, the leaf spring 206 preventing the paper from advancing or backing up to the previous posi tion.

The pawl 202 is mechanically controlled by the interposer 218 which is actuated by the solenoid which in turn is controlled by the information source. The tapes are advanced if the interposer 218 is held out to allow the pawl 202 to engage the teeth of the wheel 204 and thus drive the tapes. If the paper was advanced in the previous cycle, the interposer 218 (as shown on the timing diagram) is disengaged from the paper advance pawl 202 at the beginning of the cycle. At 38 the interposer 218 goes forward as the pawl 202 moves forward. After about 50, and assuming that the interposer solenoid 232 is excited so that the paper will move in the next cycle, the interposer solenoid withdraws the interposer 218 from the pawl 202. Otherwise, if the solenoid 232 is not energized, the interposer at the 50 point in the cycle goes forward and disables the pawl for the following cycle or cycles. if the interposer is in this latter position at the beginning of the cycle, the interposer solenoid, which is actuated at the beginning of the cycle, disengages the interposer from the advance wheel at approximately It should be noted that the paper advance moves the paper after the printing is done and brings the paper to rest right before the next printing time. Thus, the printed character on the paper is always moved out of position after printing takes place, since the interposer solenoid is excited as the code group is put into the coding chassis unit 16. It should also be noted that the interposer 218 remains virtually always in the disengaged (paper advance) position if consecutive printing is done, while the paper moves at a stopstart rate, cyclically. The interposer engages the pawl 202 for no paper advance only when a start or on timing pulse from the printer to the computer does not result in excitation of the interposer solenoid 232; thus the interposer moves only when there is a change of sequence.

Motion of the detent wheel 208 is determined by the interposer position and is employed to keep the interposer disengaged (paper advance) for a determined period of camshaft rotation after the interposer solenoid excitation is cut off at The inter-relationships between the timing of the various functions are determined mechanically. The electric control is in the pawl interposer solenoid 232 and printing wire solenoids 124 using the start timing pulse as a reference at 0 of drive shaft rotation.

The isometric view of Fig. 8A illustrates in detail the construction of the interposer actuating member 220, here shown as a channel member, having a bifurcated end portion 222 operatively engageable with the two grooves 224 224 of the interposer rod 218.

Fig. 7 is an enlarged end view of a portion of the device of Fig. 8, to show the disposition of the truncated end portion of the interposer 21.8 when it is engaged with the teeth of the wheel 204. As shown in Fig. 7, the pawl 202 is overriding the end of the interposer 218 rendering it ineffectual to operate the paper advance mechanism.

Fig. 15 is an enlarged diagrammatic sectional view of the printing head of the present invention showing the 5 x 7 matrix of printing styli. in Fig. 14 the carbon tape 30 is shown partially rolled back upon itself in order to illustrate the removal of small dots of carbon from the carbonized surface 32 of the carbon tape and the transfer and deposit thereof onto the paper tape 34.

A complete paper advance cycle for the novel thermal printer is set forth as follows:

At the start of an operating or printing cycle the pawl 202 rests on the end portion of the interposer rod 218 and is moving forward, i.e., toward the wheel 204 to engage a tooth thereof. The on pulse from the synchronizer (rotary pulser) solenoid causes the clapper 230 of the solenoid 232 to be pulled in. and withdraw the interposer rod 213 from between the teeth of the wheel 204 and from beneath the pawl 202. The notch 226 of the interposer rod now comes under the arm 216 of the detent latch 212 and drops thereinto and mechanically retains the latter in its now withdrawn position. Since the initial presence of the interposer rod prevented the pawl from en aging a tooth on wheel 204 the latter is not rotated and the tapes are not advanced. The pawl 13 202 now commences to retract to its rearward position. During the'retraction, the printing operation takes place since" the two tapes are now stationary. The pulse from the s'yn'chronizer is then generated. 8 The pawl 202 drops between adjacent: teeth of'the wheel 204 and it starts forward, rotating the wheel and advancing the two tapes.

At the start of the next cycle, if paper is not to be advanced or printing is not to be done, the pawl 202 completes its forward movement and the detent latch 212i is rocked by the teeth of the wheel 208 lifting the arm 21 6; o'ut 'of the interposer notch 226 in the interposer and permitting the same to slide between the next two teeth of the wheel 204. If the paper is to be advancedthen the'removal' of the mechanical detent 212 from the interposer has no efiect on the interposer since the "energiz'ation'of the solenoid 232 will hold the interpo er retracted. The interposer rod 218 thus is required to'inov'e only'when there is a change in sequence of operation, that isffrom paper advance to non-advance or'vice versa.

Fig. 16 is a diagrammatic view of the printing head 110 illustrated by numeral designations the wire elements used therewith. In the illustrative embodiment of Fig. 16a right hand parenthetical bracket or character is shown to be made up of the styli numbers 4, 10, 15, 20, 25, 30 and 34.

Reference is now had to Figs. 17 and 18 which illustrates one form of an electrical circuit that is adapted to selectively control the 35 electromagnetic devices 124 for operating the heated styli. A plurality of solenoides are adapted to accept signal information in the form of a'four-bit excess-three binary'code from an external signal source'such as a computer, from which the proper choice of printing wires corresponding to the particular character that the code implies is made. The electronic circuitry set forth in Fig. 17, chooses the proper set of Wires fromth'e x 7 styli matrix corresponding to the character desired.

A binary element, such for example, as used in a conventional computer possesses two stable states and may be' termed a flip-flop device. A computer may be designed to' provide a four-bit code output represented at theoutput of a group of four of the binary elements. To express a binary code any decimal digit from 0 to 9 requires four binary places. A reference to Table 1 hereinbelow will show the various possibilities, or combinations', which are available through the use of an excess-three binary code utilizing four bits. With four bits of information it is possible to represent a choice of 16" pieces of information. In the present invention the four-bit code output is fed from the computer into the' coding chassis unit 12 (Fig. 1) where a choice of one line representing a possible one of 16 choices (Table 1)"is made electrically. This choice controls the bias onlohe of '16 vacuum tubes which in turn actuates the properelectrornagnetic devices to cause the wires of the printing headto print a selected character.

Referring now to Fig. 18 is is seen that synchronization o f the printing apparatus with the output signals from a computer signal source 300 is obtained by generating a pulse from the printer at a precise moment in its cycle of op eration." This is accomplished as before mentioned by means of a rotarypulser 90, comprising a permanent magnet (Figs. 2, 3, 4, 18) in combination with a pair of stationary solenoids 102 and 104. The magnet 100 is secured to the continuously rotating drive shaft 92 by means of the support 106 formed of two similar cross arms carrying a counterbalance weight 108 on its other end. Rotation of the permanent magnet 100 past the two solenoids generates an electrornotive force (E.M.F.) in the form of separate start and stop pulses in therespective windings 102, 104 (Fig. 18) of the solenoids 102 and 104. These pulses are then reshaped respectively in start reshaper 103 and stop reshaper 105. The cycle is started as the start timing pulse signals to the computer 300 by way of lead 317 to feed a code group into the respective gate circuits 301-308. The signal from the start pulse shaper 103 simultaneously opens the gate circuits 301-308 and conditions a gang of pulse operated. relays 309-316 so that they may send control signals representing the binary computer signals intothe printer. Separate gates and relays are provided for the alternate flip-flop ouput conditions. The gates 301-308 are provided so that the computer signals are presented for the proper length of time to operate the printer circuits as determined by the signal of the pulse shaper circuit 103. It is assumed that the computer signals persist for a longer time period than that of the start pulse from shaper 103. Simultaneously the signal from the start pulse shaper conditions the paper advance relay 318v by way of lead 317 so that the paper may be advanced. Each of the relays 309-3 16 and 318 is a pulseoperated relay circuit which upon receipt of a trigger pulse at one of two leads is sent to a corresponding condition to remain inthat condition until a further pulse is received on an alternate lead. Such relays are commercially, available as a standard pulse control unit type 1801A from Burroughs Electronic Instrument Division.

The coding chassis unit 16 (Fig. 1) comprises an upper or encoding matrix 250 (Fig. 17) and a lower or decoding matrix 252- (Fig. 17). A total of 170 low current germanium diodes and 18 vacuum tubes of the dual triode type are utilized. A negative potential of minus 35 volts is supplied, from a source of potential (not shown), to one set of contacts 254 of the series of 8 input relays 309-316 of Fig. 18 by means of the line 258. Each one of the relays 309-316 is polarized and its single pole double throw switch contactor 260 is adapted to remain at rest in either of two stable states. One contact 262 of each one of the input relays is grounded through a suitable impedance 264 which may be a resistor and which serves to isolate the separate contacts of the difierent relays 309-316. These 8 relays 309-3 16 can thus be made. to signal or to indicate to the decoding matrix 252 of Fig. 18, a computer choice according to the coded output from the computer. The extra relay which is connected to the paper advance solenoid 232 (Fig. 8) hereinbefore described, is utilized to actuate the tape advance mechanism from the signal produced by contactor 321 of relay 318 over lead 321.

Since pin position 27 of Fig. 16, as before mentioned, is not used to form any of the characters chosen, in this particular embodiment the corresponding tube 27 is used to actuate the paper tape advance mechanism. The grid of this tube 27 is excited directly through lead 321 so that this grid is held either at a minus 35 volts or at 0 volts, depending upon Whether or not the tapes are advanced during any cycle of printer operation and depending upon the particular time in the cycle.

The circuit of one of the eighteen dual triodes referenced 270 is shown in schematic form in Fig. 17A at the lower right hand corner of Fig. 17. A DC. plate voltage of +250 volts is supplied from a suitable source (not shown) to the plates of the triodes by way of individual pin selecting solenoid coils, in parallel with which is a neon larnp indicator and resistance, as lamp and re- '15 sistance 127. Lamp 125 appears in panel 56 (Fig. 7). The cathode (common to the two triodes of a dual tube) identified as cathode 274, is suitably biased as to -17 volts by connection to a source of biasing potential (not shown).

In the normal or standby condition of the printer, the input lead 258 to the decoding matrix 252 is at minus 35 volts, the 13+ 250 volt plate supply is on and the cathode bias of minus 17 volts is applied to the cathode of each one of the tubes 270. All of the tubes are held at cut-off which is approximately minus 20 volts grid to cathode for the particular tube type 5687 used. Resistances 276, of suitable value, are connected in series with the encoding matrix diodes 250 and the grids of 278 of each one of the tubes 270. These latter resistors avoid large grid currents in case the grid to cathode voltage goes positive. The diodes of the encoding matrix 250 prevent feed back to the other non-selected character actuating devices when one character is chosen to be held at -17 volts and thus prevents the selection of any of the other unwanted characters.

The decoding matrix 252 is provided with a plurality of crystal diode elements similar to those of the matrix 250 and is disposed in the coding unit 16 contained in the bottom rack 24 (Fig. 1). Each one of the decoding diodes is coupled to a suitable impedance which may take the form of a resistor 280. Each decoding diode is connected between a point of common reference potential 232 and the relay contacts 254 or 262 (Fig. 17) through the 16 output leads 322-337 by means of a suitable plug or connector 286 so that either a minus 35 volt potential or a minus 20 volt potential will appear from grid to ground of each at the tubes 270.

For any one of the sixteen possible combinations of the eight on-off switch positions of the eight relays 309- 316 one, and only one, of the sixteen output leads 322- 337 will have about -17 volts; each of the other 15 will be maintained at a minus 35 volt potential through one or more of the diodes.

For an example of this, assume that a start or on pulse causes the code group 1111, corresponding to the character to be sent from the computer into the printer. To provide a signal to the matrix 252, a ground connection is necessary at the desired code input lead and conversely a negative 35 volt signal is necessary at the undesired code input lead. Thus, the solenoids of the relays 310, 3 12, 314, 316 corresponding to the inputs of the decoding matrix 252 will be energized pulling in the contactors 260 so as to place the 0 terminals at ground through the resistors 264. The contactors corresponding to the 1 inputs will be placed at minus 35 volts. The decoding matrix 252, for this particular input, causes output line 337, and only 337, to be placed at minus 17 volts, while the remaining output lines 322- 336 will be maintained at minus 35 volts through one or more of the diodes. Since the cathodes 274 of all of the tubes 270 are at approximately minus 17 volts the grid to cathode voltages of the particular set of tubes 270 numbered 4, 10, 15, 20, 26, 30 and 34 are near ground potential while all the other grid to cathode voltages are near cut-off potential or approximately minus volts for the specific tubes used. The particular tubes thus chosen can be found by following line 337, through the forward direction of the crystals of the encoding matrix 250.

The single line 337 substantially at ground potential is thus adapted to apply a potential to selected grids of the tubes 27% and to thus cause the contactors 260 of the solenoids 236 in the plate circuits thereof to be pulled in and push the heated wires to the printing position for the character After rotation of camshaft 92 through a partial revo lution, a stop pulse is generated in solenoid winding 104'. The stop signal generated through lead 319, relays 309- 318, returns relay contactors 260, 320 to the normal or disengaged condition which in turn places all of the input terminals at minus 35 volts to once more cut off all of the vacuum tubes 270. The remaining characters, as shown in the chart, set out beforehand, are each selected in substantially the same manner, depending upon the code group input to the coding chassis and at the start of the printing cylce.

What is claimed is:

1. Printing apparatus adapted to impress intelligence characters on a record receiving tape and wherein a plurality of character bearing members are caused to permanently mark a record receiving tape upon slight contact of said members against said tape comprising a supporting member for said apparatus, a pair of tapes comprising a marking tape and a record receiving tape, a first movable reel adapted to receive said marking tape, a second movable reel on the same axle with said first reel and adapted to receive said record receiving tape, drive means for said apparatus, said drive means comprising a motor, a driven shaft rotatably secured thereto, a printing head provided with a plurality of printing members adapted to form discrete intelligence characters, an adjustable backup member disposed adjacent said printing head and having a fiat printing surface, tape guide means secured adjacent to said last mentioned flat surface, means for mounting said apparatus support adapted to alter the relative position of said backup member with respect to said printing head in a plane parallel with said printing head, input signal means comprising the output signals from an information source as a computer, signal responsive members for operatively inter-connecting said printing members and said input signal means, means for synchronizing the operation of said printing members and said input signal means comprising a pair of electromagnetic members, a magnetic member secured to said driven shaft and disposed adjacent to said pair of electromagnetic members and adapted upon coincidence of said electromagnetic members and said magnetic member to produce a synchronizing pulse, means to advance said tapes intermittently, a spacer shim adjustably secured between said printing surfaces, said spacer shim being provided with an aperture for reception therethrough of said printing members, said shim being adapted to maintain said tapes in separated, parallel, superposed relationship and to permit said tapes to be brought into momentary printing contact at an area immediately adjacent the printing surface of said printing head, said means to advance said tapes intermittently including a rotatable member provided with a series of peripheral elements adapted to perforate said tapes whereby said tapes are positively moved, and visual indicating means for said printing head comprising a plurality of neon tubes.

2. In a thermal wire printer, a print head including the ends of a plurality of wires positioned for movement in a predetermined path, means for heating said printing head, means for positioning a print receiving medium adjacent said printing head, means for positioning a medium having a thermosensitive removable printing deposit formed thereon in interposed relation between said printing head and the print receiving medium, means removed from the path of movement of said wires spacing said thermosensitive medium from said print receiving medium, and control means to select certain of said wires to form a printing character and to move the ends of said selected wires first against said thermosensitive medium and then to move the latter through said space thereby to permit the heated wire ends forming the printing character to melt areas of said thermosensitive printing deposit whereby at the completion of said movement said melted deposits are transferred to said print receiving medium upon contact therewith and with the absence of impact force being applied to said print receiving medium.

3. In a thermal wire printer, a print head including the @Qds of a plurality of wires, means for heating said printing head, means for positioning a print receiving medium adjacent said printing head, means for positioning a medium having a thermosensitive removable print ing deposit formed thereon in interposed relation between said printing head and the print receiving medium, spacing means interposed between said print receiving medium and said thermosensitive medium and defining an opening opposite said printing head, and control means to select certain of said wires to form a printing character and to move the ends of said selected wires first against said thermosensitive medium and then to move the latter through the opening in said spacing means thereby to permit the heated wire ends forming the printing character to melt areas of said thermosensitive printing deposit whereby at the completion of said movement said melted deposits are transferred to said print receiving medium upon contact therewith and with the absence of impact force being applied to said print receiving medium.

4. In a thermal wire printer, means for heating and confining a plurality of wires at one end thereof to a letter printing area, said wires terminating at one end in a plane at said thermal confining means to constitute a printing face, means for advancing a print receiving medium past said printing face, means for advancing a medium having a thermosensitive removable printing deposit formed thereon in interposed relation between said printing face and the. print receiving medium, and means connected to each of said wires at their other ends for differentially adjusting the longitudinal position of selected wires to form a printing character at said printing face and to engage said thermosensitive medium whereby discrete areas of said deposit on said thermosensitive medium are melted corresponding to the end surfaces of said selected wires and are transferred to said print receiving medium with the absence of impact force being applied to said print receiving medium.

5. In a thermal wire printer, a print head comprising the ends of a plurality of wires, means for heating said printing head, means for positioning a print receiving medium adjacent said printing head, means for positioning a medium having a thermosensitive removable printing deposit formed thereon in interposed relation between said printing head and the print receiving medium, and means to select certain of said wires to form a printing character and to move the ends of said selected wires against said thermosensitive medium to move the latter against said print receiving medium and to simultaneously melt said removable deposits in dot form while so moved whereby said melted deposits are fixed to said print receiving medium in the absence of impact force being applied to said print receiving medium.

References Cited in the file of this patent UNITED STATES PATENTS 444,636 Hohenshell Jan. 13, 1891 576,146 Nickeson Feb. 2, 1897 933,181 Kavle Sept. 7, 1909 1,740,285 Correll Dec. 19, 1929 1,854,705 Luedtke Apr. 19, 1932 1,952,901 Wolff Mar. 27, 1934 2,057,696 Sherman Oct. 20, 1936 2,129,065 Loop Sept. 6, 1938 2,306,256 Wickwire Dec. 22, 1942 2,486,985 Ruderfer Nov. 1, 1949 2,501,495 Carroll Mar. 21, 1950 2,515,381 Resch July 18, 1950 2,539,303 Gerke Jan. 23, 1951 2,632,386 Hyland Mar. 24, 1953 2,639,017 Croucher May 19, 1953 2,663,252 Kingsley Dec. 22, 1953 2,681,614 Rast June 22, 1954 2,683,410 Wockenfuss July 13, 1954- 2,720,164 Braun Oct. 11, 1955 2,740,352 Kingsley Apr. 3, 1956 

